An antenna includes a first antenna element and a second antenna element, wherein the first antenna element and the second antenna element are both configured in a hook shape. The antenna also includes a first impedance matching circuit coupled to the first antenna element, wherein the first impedance matching circuit includes a first plurality of filters and a second impedance matching circuit coupled to the second antenna element, wherein the second impedance matching circuit includes a second plurality of filters.
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20. An antenna for receiving satellite signals, comprising:
a ground plane;
a first antenna element and a second antenna element, wherein the first antenna element and the second antenna element are electrically separate from one another;
a first impedance matching circuit coupled to the first antenna element, wherein the first impedance matching circuit includes a first plurality of filters; and
a second impedance matching circuit coupled to the second antenna element, wherein the second impedance matching circuit includes a second plurality of filters,
wherein the first and second antenna elements each include:
an insulating substrate having a specified thickness and a specified dielectric constant, the insulating substrate arranged in a plane substantially perpendicular to the ground plane; and
parallel components of conducting material on both sides of the insulating substrate;
each parallel component configured in a single hook shape in a plane substantially perpendicular to the ground plane;
wherein the first and second antenna elements are configured for receiving radiation that is circularly polarized.
1. An antenna for receiving satellite signals, comprising:
a ground plane;
a first antenna element and a second antenna element, wherein the first antenna element and the second antenna element are electrically separate from one another;
a first impedance matching circuit coupled to the first antenna element, wherein the first impedance matching circuit includes a first plurality of filters; and
a second impedance matching circuit coupled to the second antenna element, wherein the second impedance matching circuit includes a second plurality of filters,
wherein the first and second antenna elements each include:
an insulating substrate having a specified thickness and a specified dielectric constant, the insulating substrate arranged in a plane substantially perpendicular to the ground plane; and
parallel components of conducting material on both sides of the insulating substrate;
each parallel component configured in a single hook shape in a plane substantially perpendicular to the ground plane and including:
a first segment substantially perpendicular to the ground plane;
a second segment coupled to the first segment, extending away from a central vertical axis of the antenna, and substantially parallel to the ground plane;
a third segment coupled to the second segment and substantially perpendicular to the ground plane; and
a fourth segment coupled to the third segment and substantially parallel to the ground plane, the fourth segment extending from the third segment toward the central vertical axis of the antenna;
wherein the first and second antenna elements are configured for receiving radiation that is circularly polarized.
2. The antenna of
a respective low pass filter; and
a respective high pass filter.
3. The antenna of
4. The antenna of
5. The antenna of
at least one of the first and second antenna elements increases the gain of signals received at elevations substantially at the horizon relative to an antenna having inverted-L shaped antenna elements with radiating elements that are parallel to the ground plane.
6. The antenna of
7. The antenna of
8. The antenna of
a third antenna element and a fourth antenna element, wherein the third antenna element and the fourth antenna element are electrically distinct from one another and are both configured in a hook shape, and wherein the hook shape of each respective antenna element is formed in a plane substantially perpendicular to the ground plane;
a third impedance matching circuit coupled to the third antenna element, wherein the third impedance matching circuit includes a third plurality of filters; and
a fourth impedance matching circuit coupled to the fourth antenna element, wherein the fourth impedance matching circuit includes a fourth plurality of filters.
9. The antenna of
the first antenna element and the second antenna element are arranged substantially along a first axis of the antenna, and
the third antenna element and the fourth antenna element are arranged substantially along a second axis of the antenna.
10. The antenna of
11. The antenna of
12. The antenna of
14. The antenna of
15. The antenna of
16. The antenna of
17. The antenna of
18. The antenna of
a feed network circuit coupled to the first and second impedance matching circuits;
a low-noise amplifier coupled to the feed network circuit; and
a sampling circuit coupled to the low-noise amplifier.
19. The antenna of
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This application claims priority under 35 U.S.C. §119 to U.S. Provisional Patent Application No. 61/142,058 filed on Dec. 31, 2008, which application is incorporated by reference herein in its entirety.
This application is related to U.S. patent application Ser. No. 12/037,908, filed Feb. 26, 2008, which application is incorporated by reference herein in its entirety.
The present invention relates generally to multi-band antennas, and more specifically, to a hook shape multi-band antenna for use in global satellite positioning and communication systems.
Receivers in global navigation satellite systems (GNSS's), such as the Global Positioning System (GPS), use range measurements that are based on line-of-sight signals broadcast by satellites. The receivers measure the time-of-arrival of one or more of the broadcast signals. This time-of-arrival measurement includes a time measurement based upon a coarse acquisition coded portion of a signal, called pseudo-range, and a phase measurement.
In GPS, signals broadcast by the satellites have frequencies that are in one or several frequency bands, including an L1 band (1565 to 1585 MHz), an L2 band (1217 to 1237 MHz), an L5 band (1164 to 1189 MHz) and L-band communications (1525 to 1560 MHz). Other GNSS's broadcast signals in similar frequency bands. In order to receive one or more of the broadcast signals, receivers in GNSS's often have multiple antennas corresponding to the frequency bands of the signals broadcast by the satellites. Multiple antennas, and the related front-end electronics, add to the complexity and expense of receivers in GNSS's. In addition, the use of multiple antennas that are physically displaced with respect to one another may degrade the accuracy of the range measurements, and thus the position fix, determined by the receiver. Further, in automotive, agricultural, and industrial applications it is desirable to have a compact, rugged navigation receiver. Such a compact and rugged receiver may be mounted inside or outside a vehicle, depending on the application.
The ideal antenna for the reception of signals from GPS satellites would have a gain of 3 dB isotropic for the upper hemisphere, which sees the sky, and no gain for the lower hemisphere, which sees the earth. Additionally it would have a polarization of right hand circular (RHCP). In recent years other GNSS have supplemented the GPS signals, and their signals are best received with the same gain pattern and polarization of the ideal GPS antenna. Sometimes the accuracy of these GNSS signals are enhanced with differential corrections generated by reference receivers and transmitted on satellite downlinks at frequencies slightly lower than GPS L1. Fortunately these correction signals are also RHCP, but they tend to be of lower power and are available from fewer satellites than the GNSS signals. All together, these GNSS and communication bands cover from 1150 MHz to 1610 MHz in frequency.
Various attempts to receive all of these frequencies with an RHCP antenna having the desired gain pattern, and a moderate cost and size have been made. Most of these have gain patterns which are quite good at high elevation angles (i.e. close to straight up), but drop rapidly closer to the horizon.
There is a need, therefore, for improved compact antennas for use in receivers in GNSS's to address the problems associated with existing antennas.
Some embodiments provide an antenna including a first antenna element and a second antenna element, wherein the first antenna element and the second antenna element are both configured in a hook shape. The antenna also includes a first impedance matching circuit coupled to the first antenna element, wherein the first impedance matching circuit includes a first plurality of filters and a second impedance matching circuit coupled to the second antenna element, wherein the second impedance matching circuit includes a second plurality of filters.
In some embodiments, the antenna includes a ground plane. In these embodiments, a respective antenna element includes: a first segment substantially perpendicular to the ground plane, a second segment coupled to the first segment and substantially parallel to the ground plane, a third segment coupled to the second segment and substantially perpendicular to the ground plane, and a fourth segment coupled to the third segment and substantially parallel to the ground plane.
In some embodiments, a respective impedance matching circuit includes: a low pass filter and a high pass filter.
In some embodiments, the low pass filter and the high pass filter are coupled in series.
In some embodiments, the respective impedance matching circuit provides an impedance of substantially 50 Ohms at a center frequency of both a first frequency band and a second, higher frequency band.
In some embodiments, the antenna includes a ground plane and the first antenna element and second antenna element each have a radiating element having a predefined extent substantially parallel to the ground plane. In the embodiments, the hook shape increases the gain of signals received at elevations substantially at the horizon relative to an antenna having inverted-L shaped antenna elements with radiating elements that have the same predefined extent substantially parallel to a ground plane.
In some embodiments, the antenna includes a feed network circuit coupled to the first impedance matching circuit and the second impedance matching circuit, wherein the feed network circuit has a combined output corresponding to the signals received by the first antenna element and the second antenna element.
In some embodiments, a respective antenna element includes an insulating substrate having a specified thickness and a specified dielectric constant, and conducting material on both sides of the insulating substrate.
In some embodiments, the first antenna element and the second antenna element are arranged substantially along a first axis of the antenna.
In some embodiments, the antenna includes a third antenna element and a fourth antenna element, wherein the third antenna element and the fourth antenna element are both configured in the hook shape. The antenna also includes a third impedance matching circuit coupled to the third antenna element, wherein the third impedance matching circuit includes a third plurality of filters, and a fourth impedance matching circuit coupled to the fourth antenna element, wherein the fourth impedance matching circuit includes a fourth plurality of filters.
In some embodiments, the first antenna element and the second antenna element are arranged substantially along a first axis of the antenna. The third antenna element and the fourth antenna element are arranged substantially along a second axis of the antenna.
In some embodiments, the first axis and the second axis are substantially perpendicular to each other.
In some embodiments, the antenna includes a feed network circuit coupled to the first impedance matching circuit, the second impedance matching circuit, the third impedance matching circuit, and the fourth impedance matching circuit, wherein the feed network circuit has a combined output corresponding to the signals received by the first antenna element, the second antenna element, the third antenna element, and the fourth antenna element.
In some embodiments, the feed network circuit is configured to phase shift received signals from a respective antenna element relative to received signals from neighboring antenna elements in the antenna by substantially 90 degrees.
In some embodiments, the first antenna element, the second antenna element, the third antenna element, and the fourth antenna element are configured to receive radiation that is circularly polarized.
In some embodiments, the radiation is right hand circularly polarized radiation.
Some embodiments provide a system including an antenna, an impedance matching circuit, a feed network circuit, a low-noise amplifier, and a sampling circuit. The antenna includes a plurality of antenna elements each configured in a hook shape. The impedance matching circuit is coupled to the antenna, wherein the impedance matching circuit comprises a plurality of filters. The feed network circuit is coupled to the impedance matching circuit. The low-noise amplifier is coupled to the feed network circuit. The sampling circuit is coupled to the low-noise amplifier output.
Like reference numerals refer to corresponding parts throughout the drawings.
Reference will now be made in detail to embodiments of the invention, examples of which are illustrated in the accompanying drawings. In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be apparent to one of ordinary skill in the art that the present invention may be practiced without these specific details. In other instances, well-known methods, procedures, components, and circuits have not been described in detail so as not to unnecessarily obscure aspects of the present invention.
In this document, the terms “substantially parallel” and “substantially perpendicular” mean within five degrees (5°) of parallel or perpendicular, respectively; the term “substantially along” a particular axis means within ten degrees (10°) of the axis; the term “substantially constant impedance” means that the magnitude of the impedance varies by less than 10 percent; the term “frequency band is substantially passed” means that signals in the frequency band are attenuated in magnitude by less than 1 dB (26 percent). Values and measurements said to be “approximate” are herein defined to be within fifteen percent (15%) of the stated values or measurements.
In some embodiments, a hook shape multi-band antenna achieves a gain pattern which is more uniform in gain with respect to elevation in the upper hemisphere than a comparably sized inverted-L shape antenna, while having low gain in the lower hemisphere. The physical height of the hook shape multi-band antenna is minimized by the hook shape of the antenna elements and by the high dielectric constant of the substrate material on which the antenna elements are deposited. In some embodiments, the hook shape multi-band antenna is configured to transmit and/or receive a right hand circularly polarized (RHCP) radiation by having four identical antenna elements and a quadrature feed network circuit. Although the gain pattern is relatively uniform over the frequency bands of interest, the impedance of the antenna is not constant and is not the typical 50 ohms. Thus, in some embodiments, an impedance matching network is used on each of the four antenna elements to transform the impedance of the antenna elements at the frequency bands of interest to approximately 50 Ohms (e.g., 50 Ohms±20 Ohms) so that the signals can be transferred and processed by conventional circuitry.
The hook shape multi-band antenna covers a range of frequencies that may be too far apart to be covered using a single existing antenna. In an exemplary embodiment, the hook shape multi-band antenna is used to transmit and/or receive signal in the L1 band (1565 to 1585 MHz), the L2 band (1217 to 1237 MHz), the L5 band (1164 to 1189 MHz) and L-band communications (1525 to 1560 MHz). These four L-bands are treated as two distinct bands of frequencies: a first band of frequencies that ranges from approximately 1160 to 1252 MHz, and a second band of frequencies that ranges from approximately 1525 to 1610 MHz. Approximately center frequencies of these two bands are located at 1206 MHz (f1) and 1567 MHz (f2). These specific frequencies and frequency bands are only exemplary, and other frequencies and frequency bands may be used in other embodiments.
In some embodiments, the hook shape multi-band antenna is configured to have substantially constant impedance (sometimes called a common impedance) in the first band and the second band of frequencies. These characteristics may allow receivers in GNSS's, such as GPS, to use fewer or even one antenna to receive signals in multiple frequency bands.
While embodiments of a hook shape multi-band antenna for GPS are used as illustrative examples in the discussion that follows, it should be understood that the hook shape multi-band antenna may be applied in a variety of applications, including wireless communication, cellular telephony, as well as other GNSS's. The techniques described herein may be applied broadly to a variety of antenna types and designs for use in different ranges of frequencies.
Attention is now directed towards embodiments of the hook shape multi-band antenna.
Each of the hook shape antenna elements 102 have a total length of A1+A2+A3+A4 (e.g., a first segment, a second segment, a third segment, and a fourth segment of the antenna element 102, respectively) and B1+B2+B3+B4, respectively. Note that segments A1, A3, B1, and B3 are substantially perpendicular to the ground plane 110 and segments A2, A4, B2, and B4 are substantially parallel to the ground plane 110. Also note that “substantially parallel” is used to refer to angles within ten degrees of parallel and that “substantially perpendicular” is used to refer to angles within ten degrees of perpendicular. Referring to
Another feature of the hook shape antenna elements 102 is the fourth segments of the hook shape antenna elements 102 (e.g., A4 and B4), which turns toward the central Z-axis. These segments have the effect of pulling the gain pattern downward, hence increasing the gain at elevations closer to the horizon. Additionally, these segments add length to the antenna elements, hence improving its efficiency and extending its response to lower frequencies.
In some embodiments, the hook shape multi-band antenna 100 may include additional components or fewer components. Functions of two or more components may be combined. Positions of one or more components may be modified.
In some embodiments, the hook shape multi-band antenna 100 (
As discussed above, each of the hook shape antenna elements 102 have a total length of A1+A2+A3+A4 and B1+B2+B3+B4, respectively. Furthermore, the substrates 104 have a specified thickness 134 and a specified dielectric constant, as discussed above.
In a transmit embodiment, a 180° hybrid circuit 312 accepts an input electrical signal 310 and outputs two electrical signals that are approximately 180° out of phase with respect to one another. Each of these electrical signals is coupled to one of the 90° hybrid circuits 314. Each 90° hybrid circuit 314 outputs two electrical signals 232. A respective electrical signal, such as electrical signal 232-1, may therefore have a phase shift of approximately 90° with respect to adjacent electrical signals 232. In this configuration, the feed network circuit 300 is referred to as a quadrature feed network circuit. The phase configuration of the electrical signals 232 results in the quad hook shape multi-band antenna 200 (
In a receive embodiment, the electrical signals 232 are received by the hook shape antenna elements 102, and are combined through the feed network circuit 300, resulting in signal 310 which is provided to a receive circuit for processing. Note, the receive embodiment is the same as the transmit embodiment, but signals are processed in the opposite direction (receive, instead of transmit) as described later.
In some embodiments, the feed network circuit 300 or 380 may include additional components or fewer components. Functions of two or more components may be combined. Positions of one or more components may be modified.
Attention is now directed towards illustrative embodiments of the multi-band antenna and phase relationships that occur in the two or more frequency bands of interest. While the discussion focuses on the quad hook shape multi-band antenna 200 (
Referring to
If a substrate with a lower dielectric constant ∈ is used, and a similar gain versus elevation pattern is desired, the lengths of the conductors 106 of the hook shape antenna elements 102 will be larger for a given central frequency f1. The exact dimensions would have to be determined either by experiment or by a computer-based electromagnetic simulator. Note that the separation distance 124 between antenna elements 102 is approximately independent of ∈.
Note that the graphs in
Attention is now directed towards embodiments of processes of using a multi-band antenna with lumped element impedance matching.
In some embodiments, the method 700 of using a hook shape multi-band antenna may include fewer or additional operations. An order of the operations may be changed. At least two operations may be combined into a single operation.
The foregoing description, for purpose of explanation, has been described with reference to specific embodiments. However, the illustrative discussions above are not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many modifications and variations are possible in view of the above teachings. The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated.
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